* remove biicode support
The company/startup died in 2015 and the open source project seems
to be dead as well.
* define compiler warning flags globally instead of locally for every binary
* add support for cmake's find_package() (refs #52)
This rewrite of the main CMakeLists.txt cleans up the way ICU flags
are attached to the library target and adds the cmake helper files
(cxxopts-config.cmake, cxxopts-config-version.cmake,
cxxopts-targets.cmake) which are needed for exporting the cxxopts
target. Cmake's find_package command uses these files when the
library is consumed by another project.
Additionally, two new tests have been added which build the example
application via add_subdirectory and find_package.
* removed target_sources from interface library
Adding target_sources to interface libraries and exporting them is
not supported in CMake 3.1 and 3.2. Furthermore, since it is a header,
it is not needed at all.
* use the *_LDFLAGS instead of *_LIBARIES when linking ICU
The LIBRARIES variable seems to contain only the name and not the
full path.